Fluids of different origins and applications often have to be monitored for their chemobiological condition, which is determined, among other things, by substances being entrained in the fluid. To monitor aqueous fluids, particularly in drinking water treatment or wastewater purification plants, representative fluid samples have to be taken at sampling locations in a spatial and temporal distribution, and examined. The volume of such fluid samples generally ranges between approximately 10 ml and 500 ml.
The samples are commonly taken and dispensed by means of a sampler. U.S. Pat. Nos. 3,795,347, 3,880,011, 4,415,011, and 5,587,926, for example, disclose a sampler for dispensing a sample of a fluid withdrawn at a sampling location, said sampler comprising:                a vessel assembly                    with a tubular intake vessel for conducting a moving fluid, and            with a storage vessel for storing the fluid sample.                        
Samplers of the kind described generally include a suitable pumping device, particularly a pumping device controlled by control electronics, by means of which the fluid is caused to flow into the vessel assembly. In many cases, a vacuum pump or a displacement pump, particularly a peristaltic pump acting mechanically on the intake vessel, is used, as described, for example, in U.S. Pat. Nos. 3,880,011, 4,077,263, 4,660,607, or 5,587,926.
Furthermore, the vessel assembly of the sampler may include a metering vessel for metering a volume of the fluid sample.
Moreover, the sampler commonly comprises a single cabinet in which the vessel assembly, the pumping device, and electronic units may be mounted.
Because of the entrained substances, particularly because of bacteria, but also because of particular chemical compounds, metabolic processes take place in the fluid, which constantly change the chemobiological condition of the fluid. The change in the chemobiological condition of the fluid per unit time is commonly referred to as the activity of the fluid. The activity is temperature-dependent and increases with increasing fluid temperature and particularly also with an increasing temperature of the fluid sample.
The quality of the monitoring is determined, inter alia, by how closely the chemobiological condition of the fluid sample at the time of examination corresponds with the chemobiological condition of the fluid at the sampling instant. In many cases, however, considerable time elapses between the sampling and the examination of the sample. Therefore, the fluid samples are metered and stored in suitable storage vessels, e.g., in sample bottles.
If the fluid sample is to represent the chemobiological condition existing in the fluid at the sampling instant as precisely as possible, the activity of the fluid sample, averaged over the period between sampling and examination, must be minimized. Therefore, as shown in U.S. Pat. No. 5,587,926 or in WO-A 90 14 586, for example, the fluid samples are usually cooled to a constant storage temperature of, e.g., 4° C. (=277 K), at which a permissible activity is not exceeded.
To cool the fluid samples, the storage vessels are stored at an appropriate temperature in a cold-storage room, which, as proposed in U.S. Pat. No. 5,587,926, for example, may be provided directly in the sampler cabinet, and the fluid samples taken by the sampler are dispensed from the sampling location practically directly into the storage vessels, where they are cooled.
It has turned out, however, that with this method, the cooling rates, particularly at a fluid temperature at the sampling location of above 15° C., may be too low, so that the activity of the fluid sample until the time of examination may be too great. For example, at a fluid temperature of 16° C. and for a volume of the fluid sample of 500 ml, an average cooling rate of 1 K/h, and thus a cooling time until attaimnent of the storage temperature of 12 h, was measured. Because of the excessive activity of the fluid sample, during the dispensing and cooling, the chemobiological condition of the fluid sample may change considerably from the chemobiological condition at the sampling instant.